how to make button download going to center

<div class='row-fluid'>
    <div class='span9'>
        <div class='trans-content'>
            <div class='row-fluid'>
                <div class='span12'>
                <div class='ads-title'><h1 id='$id'>$nama_file</h1></div>
                <div class='span2 ads-info' style='margin-left: 0px;'>
                     <i class='icon-resize-full icon-white'></i>
                     $size
                </div>
                <div class='span2 ads-info' >
                    <i class='icon-time icon-white'></i>
                    $tgl
                </div>
                <div class='span2 ads-info'>
                    <i class='icon-eye-open icon-white'></i>
                    $dilihat
                </div>
                <div class='span2 ads-info'>
                    <i class='icon-file icon-white'></i>
                    $jenis
                </div>
                <div class='span2 ads-info'>
                    <i class='icon-download icon-white'></i>
                    $download
                </div>
            </div>
            <div class='row-fluid'>
                <div class='span5'>
                    <a href='download.php?id=$id' class='btn btn-block btn-success'>
                        <i class='icon-download icon-white'></i>Download
                    </a>
                </div>
            </div>
        </div>
    </div>
</div>